STANFORD UNIVERSITY
EE 350 RADIOSCIENCE SEMINAR
Professor Umran S. Inan

Winter 1998-99

Date: Wednesday, February 3, 1999
Time: 4:15-5:30 PM; Refreshments at 4:00 PM
Location: GESB 124


Auroral Effects on Meteoric Metals in the Upper Atmosphere

Craig J. Heinselman
STAR Lab, Stanford University, CA
SRI International, Menlo Park, CA

Abstract

The Leonids meteor shower of November 1998 once again attracted public attention to the field of meteor research. Although visually spectacular, even major meteor showers contribute only a small percentage to the 40 to 300 metric tons of material that is deposited each day in the earth's upper atmosphere. Meteoric phenomena have been studied for quite some time, but there remain a large number of questions with regard to the physical and chemical processes involved, due in large part to the inaccessibility of the region of the atmosphere into which material is deposited.

Another spectacular phenomenon in the upper atmosphere is the aurora Occurring in oval shaped regions around Earth's magnetic poles, aurorae also deposit energy at the same altitudes affected by meteors and can result in changes in local electron densities of two orders of magnitude or more over the course of just seconds. The auroral ovals also often have large electric fields associated with them which can transport ionized material at speeds of up to several kilometers per second.

This talk concerns coupled chemical and one-dimensional dynamical models that have been developed to investigate the impact of auroral ionization on the time evolution of meteoric iron and sodium in the upper atmosphere. Included in the models are the effects of electric fields, neutral winds, eddy diffusion, and molecular/ambipolar diffusion as well as time-varying concentrations of the relevant reactants. These models suggest that auroral processes should have a significant and measurable impact on the chemical state of the system. They also make specific predictions about the formation of sporadic E layers by dc electric fields. Radar and lidar measurements were made at the Sondrestrom Facility in Greenland to test these models. Results will be presented which are consistent with the model predictions of the effects of aurorally enhanced ionization. Measurements also show that the combined effects of electric fields, neutral winds, and ion-neutral collisions properly explain sporadic E formation and motion.